1. Field of the Invention
The present invention relates to torque wrenches for dental components. More particularly, the invention relates which to a disposable torque wrench for applying a selected maximum torque during installation of a prosthetic component onto a dental implant.
2. State of the Art
Torque wrenches are known to be useful in medicine and dentistry. For example, U.S. Pat. No. 4,304,445 to Bailey et al. discloses a "Dental Wrench" having a structure which permits application of differing torques to the bur securing collet of a dental handpiece and the end cap of a turbine housing in a single wrench assembly. The Bailey et al. wrench has a shaft which engages the bur securing collet, and which is supported rotatively in a frame member and secured to a support member which has means for engaging the end cap of the turbine housing. Interlocking means are provided between the support member and the frame member so that the wrench can be rotated as a unitary assembly to secure or remove the end cap of a turbine housing. The interlocking means are releasable so that the shaft can be rotated independently within the frame member to secure or remove a dental bur in or from the collet of the handpiece housing. That portion of the frame member which is gripped for securing the end cap of the housing is of larger diameter relative to the support member so that increased torque can be applied to the end cap when the interlocking means is engaged to securely fasten the cap to the housing.
Another dental torque wrench with a similar purpose is disclosed in U.S. Pat. No. 3,935,761 to Junkel et al. The torque wrench of Junkel et al. includes a unitary angular C-shaped body, one of the arms of the body being provided with a socket, and a recess for accurately locating the wrench in position relative to the head of a handpiece when chuck adjustment (or removal) is desired. Between the paired arms is a knurled cylindrical wheel dimensioned to fit comfortably between, and be rotated by, the same fingers that receive the narrower connecting portion of the C-shaped body. A torsion spring shaft extends through the wheel and into the socket and has a non-circular end portion receivable with in opening of a handpiece chuck for locking the two parts (chuck and shaft) against independent relative rotation. A shoulder of the shaft limits the extent that the end portion may be inserted into the chuck opening, and the substantial length of that shaft, and its relationship with the other parts of the wrench, result in a torsional flexure of the shaft upon chuck tightening that signals the user when the torque limit is approached. The shaft is spring-loaded for limited axial movement.
In addition to torque wrenches designed for adjusting dental tools, there are known torque wrenches for applying torque to dental implants, posts and other components. For example, U.S. Pat. No. 4,480,997 (reissue 31948) to Deutsch et al. discloses a "Dental Post and Wrench Therefor and Method of Restoring Bulk to a Tooth Root Therewith". This known wrench is used to apply a predetermined torque to a dental post to thread it into the tooth root for crown restoration. The wrench is small and designed to be manipulated with thumb and index finger. It has a manually rotatable driving handle, the interior of which is hollowed to form a chamber. The lower end of the chamber terminates in a closure wall that has a centrally located opening through which a driven shaft extends outwardly from the handle. The driven shaft has an enlarged head, the undersurface of which provides a clutch or engaging surface that engages with the facing engaging surface of the closure wall. The engaging surfaces of the head and the closure wall function as clutch means to transmit the drive from the drive handle to the driven shaft.
The known torque wrenches for use in dentistry are relatively complex and expensive, difficult to calibrate, and require repeated sterilizations. They all require either a clutch means, a spring loading, or interacting parts movable relative to each other. For the purpose of applying a maximum torque to a dental component, however, the ideal wrench is compact, simply constructed, inexpensive, easy to use, and disposable. It should have few, if any, relatively moving parts.